Geomorphological habitat type drives variation in temporal species
turnover but not temporal nestedness in Amazonian fish assemblages
Abstract
Explaining the mechanisms underlying spatial and temporal variation in
community composition is a major challenge. Nevertheless, the processes
controlling temporal variation at a site (i.e., temporal β-diversity,
including its turnover and nestedness components) are less understood
than those affecting variation among sites (i.e., spatial β-diversity).
Short-term temporal turnover (e.g., throughout an annual cycle) is
expected to correlate positively with seasonal environmental variability
and landscape connectivity, but also species pool size (γ-diversity). We
use the megadiverse Amazonian freshwater ichthyofauna as a model to ask
whether seasonality and landscape connectivity drive variation in
temporal species turnover among geomorphological habitat types, while
taking into account between-habitat variation in γ-diversity. 11,397
fish representing 260 species were collected during a year-long sampling
program in an area containing the lowland Amazon’s four major
geomorphological habitat types: rivers, floodplains, terra firme
streams, and shield streams. River-floodplain systems exhibit strong but
predictable seasonality (via a high-amplitude annual flood pulse), high
connectivity, and high species richness with many rare species. Terra
firme and shield streams exhibit low seasonality, low connectivity, and
low species richness with proportionally fewer rare species. Based on
these parameters we predicted that river-floodplain systems should have
higher temporal turnover than stream systems. Using a null model
approach combined with β-deviation calculations, we confirmed that
rivers and floodplains do exhibit higher turnover (but not nestedness)
than terra firme and shield streams, even when controlling for the
potentially confounding effect of higher species richness in
river-floodplain systems. All habitats exhibit low temporal nestedness,
indicating that short-term changes in community composition result
primarily from temporal species turnover. Our results provide a timely
reminder that efforts to conserve the Amazon’s threatened aquatic
biodiversity should account for the distinct temporal dynamics of
habitat types and variation in hydrological seasonality.